Vaillant EcoTec Fault F28

AlwaysSomething

Hi all,
I am looking after a house which is currently empty. It has a Vaillant Eco Tec boiler, and the central heating is left on. It developed a very small leak - just a small drip. This caused the pressure to drop, and the system shut off with fault code F25 - low pressure. I took care of the leak, and topped up the system using the filler loop. Now it won't fire up. It makes all the whirring sounds of starting up, but I get a fault F28 - failure to ignite.
I can look in the book, and see the possible causes (there are several). My question is for the experts. The house is empty, so no-one is using gas for anything else, and no hot water. The boiler was working fine, and it didn't shut off with F28, it shut off because of low water pressure in the heating. Can you say what is the most likely problem, and is there anything I can do to test, or help the system?
Thanks

ormus

failure to ignite can be due to lots of reasons.
pump failure is fairly common.

gas4you

is it cold where you are?

Condensate blocked or frozen can throw up F28 on these.

AlwaysSomething

gas4you wrote: »

is it cold where you are?

Condensate blocked or frozen can throw up F28 on these.

Thermostat was reading 10 degrees, and no ice around. It's only a short run to the drain too. I doubt that's the problem.